An optical source can be a cost-effective way of obtaining certain information from a substance by penetrating the surface, or surfaces, of a substance, and being subsequently scattered or reflected by the surface or surfaces. As described herein, surfaces includes interior surfaces within a substance. This scatter or reflection can be used to provide useful information with respect to the depth profile or physical structure of the surface. For example, certain medical imaging techniques can measure the reflectivity as a function of depth, and use this information to produce a three-dimensional image of a substance. To accurately measure the reflectivity, the scattered or reflected signal can be interfered with a reference beam, producing an output beam, that projects an interference pattern which is interpreted by an interferometer or other detector. These interference patterns are typically made up of multiple signal fringes and each signal fringe typically represents a depth of penetration value of the optical source into the substance. These multiple depth penetration values are used to generate a depth profile of the substance.
Optical coherence tomography (OCT) is one such imaging technique, used to obtain depth information of a substance. In OCT systems, light is typically split into a sample beam and a reference beam, the sample beam being projected onto the substance and being reflected or scattered off the surface or surfaces of the substance. The reflected or scattered beam is collimated to form a return beam, the return beam being interfered with the reference beam to generate an output beam, the output beam projecting an interference pattern onto an interferometer, for example, a CCD sensor, from which aspects of the structure of a substance can be obtained, for example the depth of various surfaces in the substance.
OCT systems generally fall into spectral domain and time domain systems. Time domain OCT (TDOCT) systems scan over a range of reference arm delays (often by moving a mirror) to allow for reconstruction of a depth profile. Spectral Domain OCT (SD OCT) systems examine the interference pattern as a function of wavelength (often by dispersing a broadband signal) as an alternative means of reconstructing the depth profile. The interference pattern as a function of wavelength can also be sampled by sweeping the wavelength of the light in the interferometer, often called Swept Source OCT (SSOCT). Theses reconstructed depth profiles can provide information on the structure of the examined substance.
Confocal imaging is a technique in which light outside of the imaging focal plane is not detected due to a pinhole located at the focal point in a conjugate focal plane. The resulting image is a thin slice of the sample object where the thickness is proportional to the diameter of the pinhole. Since out-of-plane light is generally disregarded, the image can be effectively de-blurred and the spatial resolution can be increased. A full three-dimensional image reconstruction can also be possible with a confocal system by imaging different slices independently and then stacking the slices in the appropriate order. Confocal systems are typically implemented as a microscope.
In each of OCT systems and confocal imaging systems, signal losses can occur due to the particular optical components used and their respective arrangement. For example, beam splitters can introduce losses. Typically, the beam splitter first splits the input beam forming a reference beam and a sample beam, the reference beam being the portion of the input beam reflected by the beam splitter and the sample beam being the portion transmitted through the beam splitter. The sample beam is projected onto a substance and is reflected or scattered off the surface, or surfaces, of the substance. This reflected or scattered beam is then collimated to form a return beam. The return beam projecting back to the same beam splitter, while the reference beam, originally generated by the beam splitter, is reflected back toward the same beam splitter by a reflective surface. The same beam splitter then can generate an output beam, the output beam being an interference beam generated by interfering the reference beam with the return beam by the same beam splitter reflecting a portion of the return beam and transmitting a portion of the reference beam through the beam splitter; however, losses in the signal occur due to a portion of the return beam being transmitted through the beam splitter, along with a portion of the reference beam being reflected by the beam splitter, these portions being directed back toward the input source. The beam portions directed back to the input source additionally interfere with the input source, causing signal losses in the output signal.
Some existing OCT and confocal imaging systems have boosted the optical power of the input beam to improve the resulting signal intensity of the resulting output signal. In such systems the same losses occur, but a desired intensity signal of the output beam intensity can be generated at a cost of additional energy due to the increased intensity of the input signal. Devices that provide improvements in output beam signal intensity can additionally provide an energy savings benefit, since an input beam of a lower signal intensity can produce an output beam of a desired signal intensity.
OCT and confocal imaging systems that avoid using optical elements in ways that generate signal losses, for example, using the same beam splitter to both split an input beam and generate an output beam, can reduce signal losses. OCT and confocal imaging systems using axicon lenses can use the axicon lens to bypass beam splitters and other optical elements, and in some embodiments replacing beam splitters, to reduce signal losses in the system and increase the total output signal intensity which can improve the quality of the system and can provide energy savings.